Abstract : Performance of subjects on a set of two-dimensional velocity control acquisition tasks was measured when the control was operated by thumb, hand, and forearm. Four control conditions--high and low sensitivity with 0 and 2 sec exponential lag--were used. Six groups, each of 6 naval ratings, acted as subjects; and the three limb-segments were compared under all conditions. It was found that, under the easiest condition, there was no significant difference between the controls; but in the most difficult, hand was superior to both forearm (p<0.001) and thumb (p<0.01), whilst thumb was superior to forearm (p<0.01). (Author)